The purpose of this project is to obtain information pertaining to the structure and diversity of HIV with respect to its biochemical, pathogenic, and immunological variability. Heterogeneity among retroviral genomes is a distinct feature of Lentiviruses. The human immunodeficiency virus type 1 Lentivirus (HIV-1), the causative agent of acquired immunodeficiency syndrome, has been isolated from CD4 positive peripheral blood lymphocytes (PBLs) and monocyte derived macrophages (MDMs) of sero-positive individuals. Stable infectious molecular clones of HIV-1, which generate high titers of virus capable of infecting cultured PBLs, MDMs and a variety of CD4 positive T cell leukemic lines have been extensively used to delineate the structure and function of HIV-1-encoded proteins. Since HIV-1 causes infections in humans and chimpanzees and induces disease only in humans, chimeric simian/human immunodeficiency viruses (SHIVs) have been constructed to examine the pathogenicity pertaining to HIV-1-encoded proteins in a Rhesus macaque model system. Presently, we are trying to molecularly clone a highly infectious SHIV (DH-12R) swarm from monkey PBLs. This highly pathogenic SHIV (DH-12R) with acute CD4 depletion emerged following treatment of a Rhesus macaque with an anti-CD8 monoclonal antibody that was challenged with SHIV (DH-12). To obtain a pathogenic SHIV molecular clone, Hirt DNA samples were prepared from DH-12R infected Rhesus PBLs and/or infected tissue, ligated to Lambda phage vectors (EMBL4 and gt Wesb) and analyzed by hybridization and probed. Of the clones obtained, most were full length but contained defects. The 5' and 3' halves of several of these proviral DNA clones, in which certain genes were intact and contained no deletions, are being used to construct 2-LTR full length molecular clones by mixing and matching between the 5-prime and and 3-prime ends. These molecular clones are being tested for both infectivity in tissue culture as well as their ability to induce disease in inoculated macaque monkeys.